Photoelectric UBV observations of 1782 stars are used to explore properties of the HK objective-prism survey conducted by Beers, Preston, and Shectman with the Curtis-Schmidt telescope of the Cerro Tololo Inter-American Observatory. We construct an intrinsic (U-B)0 versus (B-V)0 relation for blue horizontal branch stars and use it to derive estimates of E(B-V) color excesses in 50 survey fields. Comparison of these with the reddening maps of Burstein and Heiles indicates good agreement except in low-latitude fields toward the Galactic bulge. We describe qualitative features of the stellar content of the HK survey by use of unreddened two-color diagrams and indicate how the photometric data may prove useful in several applications. Finally, we use a halo density model to estimate the variation of completeness with apparent magnitude, B, in our catalog of field horizontal branch star candidates.
V-band photometric follow-up of RR Lyrae from SEKBO
Short Name:
J/ApJ/756/23
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate the steepening of the power-law slope beyond the Galactocentric radius of R~45kpc in the RR Lyrae (RRL) space density distribution found by Keller et al. (2008, Cat. J/ApJ/678/851). They identified 2016 RRL candidates derived from the analysis of archival observations of the Southern Edgeworth-Kuiper Belt Object (SEKBO) survey. Our aim is to verify the completeness of RRLs and ultimately the space density distribution function given by Keller et al. We followed up on a subset of 137 candidates with a range of magnitudes (V~14-20) using the Faulkes Telescope (FT) database and confirmed 57 candidates as real RRLs. A cross-match between SEKBO RRL survey and Sloan Digital Sky Survey Data Release-7 (SDSS DR-7) revealed 272 RRL candidates in common. Applying the color selection criteria proposed by Ivezi\'c et al. (2005AJ....129.1096I) resulted in 193 likely RRLs. The completeness as a function of magnitude was calculated empirically from the combined set of SEKBO RRL candidates from current FT data, SDSS cross-matched data, and the Prior et al. catalog (2009, Cat. J/ApJ/691/306). This resulted in a spatial density distribution characterized by two power laws with a break radius R within a range between 45kpc and 50kpc, similar to the results of Keller et al. We find the power-law slopes for the inner halo as n_inner_=-2.78+/-0.02 and for the outer halo as n_outer_=-5.0+/-0.2.
We present evidence for a ring of stars in the plane of the Milky Way, extending at least from l=180{deg} to 227{deg} with turnoff magnitude g~19.5; the ring could encircle the Galaxy. We infer that the low Galactic latitude structure is at a fairly constant distance of R=18+/-2kpc from the Galactic center above the Galactic plane and has R=20+/-2kpc in the region sampled below the Galactic plane. The evidence includes 500 Sloan Digital Sky Survey spectroscopic radial velocities of stars within 30{deg} of the plane. The velocity dispersion of the stars associated with this structure is found to be 27km/s at (l, b)=(198, -27), 22km/s at (l, b)=(225, 28), 30km/s at (l, b)=(188, 24), and 30km/s at (l, b)=(182, 27). The structure rotates in the same prograde direction as the Galactic disk stars but with a circular velocity of 110+/-25km/s. The narrow measured velocity dispersion is inconsistent with power-law spheroid or thick-disk populations.
